The purpose of these investigations is to determine the hemodynamic changes that occur in partially obstructed coronary arteries. Using a technique we have developed for producing controlled amounts of fixed partial obstruction, we will investigate the phasic changes in coronary blood flow that occur with stenosis in the coronary artery. We have shown that periodic cyclical reductions occur in coronary blood flow, when the coronary artery has been given a 60-80% stenosis. We believe that this is due to platelet aggregation in the narrowed lumen, and have shown that it can be abolished with aspirin. We intend to pursue preliminary studies of catecholamine and fatty acid infusions, which appear to exacerbate this phenomenon and to look for agents other than aspirin which may prevent it. We speculate that if this phenomenon occurs in the diseased stenotic coronary arteries of man, it may produce angina and sudden death.